diff mbox

[v4,3/4] Introduce & use new lightweight SGL iterators

Message ID 1463704290-3491-3-git-send-email-david.s.gordon@intel.com (mailing list archive)
State New, archived
Headers show

Commit Message

Dave Gordon May 20, 2016, 12:31 a.m. UTC 
The existing for_each_sg_page() iterator is somewhat heavyweight, and is
limiting i915 driver performance in a few benchmarks. So here we
introduce somewhat lighter weight iterators, primarily for use with GEM
objects or other case where we need only deal with whole aligned pages.

Unlike the old iterator, the new iterators use an internal state
structure which is not intended to be accessed by the caller; instead
each takes as a parameter an output variable which is set before each
iteration. This makes them particularly simple to use :)

One of the new iterators provides the caller with the DMA address of
each page in turn; the other provides the 'struct page' pointer required
by many memory management operations.

Various uses of for_each_sg_page() are then converted to the new macros.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h         | 62 +++++++++++++++++++++++++--
 drivers/gpu/drm/i915/i915_gem.c         | 20 ++++-----
 drivers/gpu/drm/i915/i915_gem_fence.c   | 14 +++---
 drivers/gpu/drm/i915/i915_gem_gtt.c     | 76 ++++++++++++++++-----------------
 drivers/gpu/drm/i915/i915_gem_userptr.c |  7 ++-
 5 files changed, 116 insertions(+), 63 deletions(-)

Comments

Chris Wilson May 20, 2016, 8:15 a.m. UTC | #1 
On Fri, May 20, 2016 at 01:31:29AM +0100, Dave Gordon wrote:
> The existing for_each_sg_page() iterator is somewhat heavyweight, and is
> limiting i915 driver performance in a few benchmarks. So here we
> introduce somewhat lighter weight iterators, primarily for use with GEM
> objects or other case where we need only deal with whole aligned pages.
> 
> Unlike the old iterator, the new iterators use an internal state
> structure which is not intended to be accessed by the caller; instead
> each takes as a parameter an output variable which is set before each
> iteration. This makes them particularly simple to use :)
> 
> One of the new iterators provides the caller with the DMA address of
> each page in turn; the other provides the 'struct page' pointer required
> by many memory management operations.
> 
> Various uses of for_each_sg_page() are then converted to the new macros.
> 
> Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h         | 62 +++++++++++++++++++++++++--
>  drivers/gpu/drm/i915/i915_gem.c         | 20 ++++-----
>  drivers/gpu/drm/i915/i915_gem_fence.c   | 14 +++---
>  drivers/gpu/drm/i915/i915_gem_gtt.c     | 76 ++++++++++++++++-----------------
>  drivers/gpu/drm/i915/i915_gem_userptr.c |  7 ++-
>  5 files changed, 116 insertions(+), 63 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 6894d8e..01cde0f 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2120,6 +2120,10 @@ struct drm_i915_gem_object_ops {
>  #define INTEL_FRONTBUFFER_ALL_MASK(pipe) \
>  	(0xff << (INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe)))
>  
> +void i915_gem_track_fb(struct drm_i915_gem_object *old,
> +		       struct drm_i915_gem_object *new,
> +		       unsigned frontbuffer_bits);
> +

That's not a much better spot, since this is now before the object it
acts upon. One day we'll get our types separated from their actors.

>  struct drm_i915_gem_object {
>  	struct drm_gem_object base;
>  
> @@ -2251,9 +2255,61 @@ struct drm_i915_gem_object {
>  };
>  #define to_intel_bo(x) container_of(x, struct drm_i915_gem_object, base)
>  
> -void i915_gem_track_fb(struct drm_i915_gem_object *old,
> -		       struct drm_i915_gem_object *new,
> -		       unsigned frontbuffer_bits);
> +/*
> + * New optimised SGL iterator for GEM objects
> + */
> +struct sgt_iter {
> +	struct scatterlist *sgp;
> +	union {
> +		unsigned long pfn;
> +		unsigned long dma;
> +	} ix;

An anonymous union here would be slightly more pleasant. And we should
be using the correct types.

> +	unsigned int curr;
> +	unsigned int max;
> +};
> +
> +/* Constructor for new iterator */
> +static inline struct sgt_iter
> +__sgt_iter(struct scatterlist *sgl, bool dma)
> +{
> +	struct sgt_iter s = { .sgp = sgl };
> +
> +	if (s.sgp) {

Not acceptable just to GPF out if passed in a NULL? It's a BUG for all
our use cases. And would save a conditional every chain step.

> +		s.max = s.curr = s.sgp->offset;
> +		s.max += s.sgp->length;
> +		if (dma)
> +			s.ix.dma = sg_dma_address(s.sgp);
> +		else
> +			s.ix.pfn = page_to_pfn(sg_page(s.sgp));
> +	}
> +
> +	return s;
> +}
> +
> +/**
> + * for_each_sgt_dma - iterate over the DMA addresses of the given sg_table
> + * @__dmap:	DMA address (output)
> + * @__iter:	'struct sgt_iter' (iterator state, internal)
> + * @__sgt:	sg_table to iterate over (input)
> + */
> +#define for_each_sgt_dma(__dmap, __iter, __sgt)				\
> +	for ((__iter) = __sgt_iter((__sgt)->sgl, true);			\
> +	     ((__dmap) = (__iter).ix.dma + (__iter).curr);		\

This prevents us using dma_addr_t 0, which is the error value iirc, so ok.

> +	     (((__iter).curr += PAGE_SIZE) < (__iter).max) ||		\
> +		((__iter) = __sgt_iter(sg_next((__iter).sgp), true), 0))
> +
> +/**
> + * for_each_sgt_page - iterate over the pages of the given sg_table
> + * @__pp:	page pointer (output)
> + * @__iter:	'struct sgt_iter' (iterator state, internal)
> + * @__sgt:	sg_table to iterate over (input)
> + */
> +#define for_each_sgt_page(__pp, __iter, __sgt)				\
> +	for ((__iter) = __sgt_iter((__sgt)->sgl, false);		\
> +	     ((__pp) = (__iter).ix.pfn == 0 ? NULL :			\
> +	           pfn_to_page((__iter).ix.pfn + ((__iter).curr >> PAGE_SHIFT)));\

If we shifted in the __sgt_iter() we could do simpler instructions inside
the loop. The compiler won't know that pfn_to_page() is always true, so
maybe a pfn_to_page(),1 here will help?

> +	     (((__iter).curr += PAGE_SIZE) < (__iter).max) ||		\
> +		((__iter) = __sgt_iter(sg_next((__iter).sgp), false), 0))
diff mbox

Patch

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 6894d8e..01cde0f 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2120,6 +2120,10 @@  struct drm_i915_gem_object_ops {
 #define INTEL_FRONTBUFFER_ALL_MASK(pipe) \
 	(0xff << (INTEL_FRONTBUFFER_BITS_PER_PIPE * (pipe)))
 
+void i915_gem_track_fb(struct drm_i915_gem_object *old,
+		       struct drm_i915_gem_object *new,
+		       unsigned frontbuffer_bits);
+
 struct drm_i915_gem_object {
 	struct drm_gem_object base;
 
@@ -2251,9 +2255,61 @@  struct drm_i915_gem_object {
 };
 #define to_intel_bo(x) container_of(x, struct drm_i915_gem_object, base)
 
-void i915_gem_track_fb(struct drm_i915_gem_object *old,
-		       struct drm_i915_gem_object *new,
-		       unsigned frontbuffer_bits);
+/*
+ * New optimised SGL iterator for GEM objects
+ */
+struct sgt_iter {
+	struct scatterlist *sgp;
+	union {
+		unsigned long pfn;
+		unsigned long dma;
+	} ix;
+	unsigned int curr;
+	unsigned int max;
+};
+
+/* Constructor for new iterator */
+static inline struct sgt_iter
+__sgt_iter(struct scatterlist *sgl, bool dma)
+{
+	struct sgt_iter s = { .sgp = sgl };
+
+	if (s.sgp) {
+		s.max = s.curr = s.sgp->offset;
+		s.max += s.sgp->length;
+		if (dma)
+			s.ix.dma = sg_dma_address(s.sgp);
+		else
+			s.ix.pfn = page_to_pfn(sg_page(s.sgp));
+	}
+
+	return s;
+}
+
+/**
+ * for_each_sgt_dma - iterate over the DMA addresses of the given sg_table
+ * @__dmap:	DMA address (output)
+ * @__iter:	'struct sgt_iter' (iterator state, internal)
+ * @__sgt:	sg_table to iterate over (input)
+ */
+#define for_each_sgt_dma(__dmap, __iter, __sgt)				\
+	for ((__iter) = __sgt_iter((__sgt)->sgl, true);			\
+	     ((__dmap) = (__iter).ix.dma + (__iter).curr);		\
+	     (((__iter).curr += PAGE_SIZE) < (__iter).max) ||		\
+		((__iter) = __sgt_iter(sg_next((__iter).sgp), true), 0))
+
+/**
+ * for_each_sgt_page - iterate over the pages of the given sg_table
+ * @__pp:	page pointer (output)
+ * @__iter:	'struct sgt_iter' (iterator state, internal)
+ * @__sgt:	sg_table to iterate over (input)
+ */
+#define for_each_sgt_page(__pp, __iter, __sgt)				\
+	for ((__iter) = __sgt_iter((__sgt)->sgl, false);		\
+	     ((__pp) = (__iter).ix.pfn == 0 ? NULL :			\
+	           pfn_to_page((__iter).ix.pfn + ((__iter).curr >> PAGE_SHIFT)));\
+	     (((__iter).curr += PAGE_SIZE) < (__iter).max) ||		\
+		((__iter) = __sgt_iter(sg_next((__iter).sgp), false), 0))
 
 /**
  * Request queue structure.
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5797fa2..6aab0b8 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2165,7 +2165,8 @@  static void i915_gem_object_free_mmap_offset(struct drm_i915_gem_object *obj)
 static void
 i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
 {
-	struct sg_page_iter sg_iter;
+	struct sgt_iter sgt_iter;
+	struct page *page;
 	int ret;
 
 	BUG_ON(obj->madv == __I915_MADV_PURGED);
@@ -2187,9 +2188,7 @@  static void i915_gem_object_free_mmap_offset(struct drm_i915_gem_object *obj)
 	if (obj->madv == I915_MADV_DONTNEED)
 		obj->dirty = 0;
 
-	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
-		struct page *page = sg_page_iter_page(&sg_iter);
-
+	for_each_sgt_page(page, sgt_iter, obj->pages) {
 		if (obj->dirty)
 			set_page_dirty(page);
 
@@ -2246,7 +2245,7 @@  static void i915_gem_object_free_mmap_offset(struct drm_i915_gem_object *obj)
 	struct address_space *mapping;
 	struct sg_table *st;
 	struct scatterlist *sg;
-	struct sg_page_iter sg_iter;
+	struct sgt_iter sgt_iter;
 	struct page *page;
 	unsigned long last_pfn = 0;	/* suppress gcc warning */
 	int ret;
@@ -2343,8 +2342,8 @@  static void i915_gem_object_free_mmap_offset(struct drm_i915_gem_object *obj)
 
 err_pages:
 	sg_mark_end(sg);
-	for_each_sg_page(st->sgl, &sg_iter, st->nents, 0)
-		put_page(sg_page_iter_page(&sg_iter));
+	for_each_sgt_page(page, sgt_iter, st)
+		put_page(page);
 	sg_free_table(st);
 	kfree(st);
 
@@ -2403,7 +2402,8 @@  static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
 {
 	unsigned long n_pages = obj->base.size >> PAGE_SHIFT;
 	struct sg_table *sgt = obj->pages;
-	struct sg_page_iter sg_iter;
+	struct sgt_iter sgt_iter;
+	struct page *page;
 	struct page *stack_pages[32];
 	struct page **pages = stack_pages;
 	unsigned long i = 0;
@@ -2420,8 +2420,8 @@  static void *i915_gem_object_map(const struct drm_i915_gem_object *obj)
 			return NULL;
 	}
 
-	for_each_sg_page(sgt->sgl, &sg_iter, sgt->nents, 0)
-		pages[i++] = sg_page_iter_page(&sg_iter);
+	for_each_sgt_page(page, sgt_iter, sgt)
+		pages[i++] = page;
 
 	/* Check that we have the expected number of pages */
 	GEM_BUG_ON(i != n_pages);
diff --git a/drivers/gpu/drm/i915/i915_gem_fence.c b/drivers/gpu/drm/i915/i915_gem_fence.c
index a2b938e..2b6bdc2 100644
--- a/drivers/gpu/drm/i915/i915_gem_fence.c
+++ b/drivers/gpu/drm/i915/i915_gem_fence.c
@@ -745,15 +745,15 @@  void i915_gem_restore_fences(struct drm_device *dev)
 void
 i915_gem_object_do_bit_17_swizzle(struct drm_i915_gem_object *obj)
 {
-	struct sg_page_iter sg_iter;
+	struct sgt_iter sgt_iter;
+	struct page *page;
 	int i;
 
 	if (obj->bit_17 == NULL)
 		return;
 
 	i = 0;
-	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
-		struct page *page = sg_page_iter_page(&sg_iter);
+	for_each_sgt_page(page, sgt_iter, obj->pages) {
 		char new_bit_17 = page_to_phys(page) >> 17;
 		if ((new_bit_17 & 0x1) !=
 		    (test_bit(i, obj->bit_17) != 0)) {
@@ -775,7 +775,8 @@  void i915_gem_restore_fences(struct drm_device *dev)
 void
 i915_gem_object_save_bit_17_swizzle(struct drm_i915_gem_object *obj)
 {
-	struct sg_page_iter sg_iter;
+	struct sgt_iter sgt_iter;
+	struct page *page;
 	int page_count = obj->base.size >> PAGE_SHIFT;
 	int i;
 
@@ -790,8 +791,9 @@  void i915_gem_restore_fences(struct drm_device *dev)
 	}
 
 	i = 0;
-	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
-		if (page_to_phys(sg_page_iter_page(&sg_iter)) & (1 << 17))
+
+	for_each_sgt_page(page, sgt_iter, obj->pages) {
+		if (page_to_phys(page) & (1 << 17))
 			__set_bit(i, obj->bit_17);
 		else
 			__clear_bit(i, obj->bit_17);
diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
index 7eab619..4668477 100644
--- a/drivers/gpu/drm/i915/i915_gem_gtt.c
+++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
@@ -1839,20 +1839,19 @@  static void gen6_ppgtt_insert_entries(struct i915_address_space *vm,
 				      enum i915_cache_level cache_level, u32 flags)
 {
 	struct i915_hw_ppgtt *ppgtt = i915_vm_to_ppgtt(vm);
-	gen6_pte_t *pt_vaddr;
 	unsigned first_entry = start >> PAGE_SHIFT;
 	unsigned act_pt = first_entry / GEN6_PTES;
 	unsigned act_pte = first_entry % GEN6_PTES;
-	struct sg_page_iter sg_iter;
+	gen6_pte_t *pt_vaddr = NULL;
+	struct sgt_iter sgt_iter;
+	dma_addr_t addr;
 
-	pt_vaddr = NULL;
-	for_each_sg_page(pages->sgl, &sg_iter, pages->nents, 0) {
+	for_each_sgt_dma(addr, sgt_iter, pages) {
 		if (pt_vaddr == NULL)
 			pt_vaddr = kmap_px(ppgtt->pd.page_table[act_pt]);
 
 		pt_vaddr[act_pte] =
-			vm->pte_encode(sg_page_iter_dma_address(&sg_iter),
-				       cache_level, true, flags);
+			vm->pte_encode(addr, cache_level, true, flags);
 
 		if (++act_pte == GEN6_PTES) {
 			kunmap_px(ppgtt, pt_vaddr);
@@ -1861,6 +1860,7 @@  static void gen6_ppgtt_insert_entries(struct i915_address_space *vm,
 			act_pte = 0;
 		}
 	}
+
 	if (pt_vaddr)
 		kunmap_px(ppgtt, pt_vaddr);
 }
@@ -2362,22 +2362,20 @@  static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
 {
 	struct drm_i915_private *dev_priv = to_i915(vm->dev);
 	struct i915_ggtt *ggtt = i915_vm_to_ggtt(vm);
-	unsigned first_entry = start >> PAGE_SHIFT;
-	gen8_pte_t __iomem *gtt_entries =
-		(gen8_pte_t __iomem *)ggtt->gsm + first_entry;
-	int i = 0;
-	struct sg_page_iter sg_iter;
-	dma_addr_t addr = 0; /* shut up gcc */
+	struct sgt_iter sgt_iter;
+	gen8_pte_t __iomem *gtt_entries;
+	gen8_pte_t gtt_entry;
+	dma_addr_t addr;
 	int rpm_atomic_seq;
+	int i = 0;
 
 	rpm_atomic_seq = assert_rpm_atomic_begin(dev_priv);
 
-	for_each_sg_page(st->sgl, &sg_iter, st->nents, 0) {
-		addr = sg_dma_address(sg_iter.sg) +
-			(sg_iter.sg_pgoffset << PAGE_SHIFT);
-		gen8_set_pte(&gtt_entries[i],
-			     gen8_pte_encode(addr, level, true));
-		i++;
+	gtt_entries = (gen8_pte_t __iomem *)ggtt->gsm + (start >> PAGE_SHIFT);
+
+	for_each_sgt_dma(addr, sgt_iter, st) {
+		gtt_entry = gen8_pte_encode(addr, level, true);
+		gen8_set_pte(&gtt_entries[i++], gtt_entry);
 	}
 
 	/*
@@ -2388,8 +2386,7 @@  static void gen8_ggtt_insert_entries(struct i915_address_space *vm,
 	 * hardware should work, we must keep this posting read for paranoia.
 	 */
 	if (i != 0)
-		WARN_ON(readq(&gtt_entries[i-1])
-			!= gen8_pte_encode(addr, level, true));
+		WARN_ON(readq(&gtt_entries[i-1]) != gtt_entry);
 
 	/* This next bit makes the above posting read even more important. We
 	 * want to flush the TLBs only after we're certain all the PTE updates
@@ -2440,20 +2437,20 @@  static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
 {
 	struct drm_i915_private *dev_priv = to_i915(vm->dev);
 	struct i915_ggtt *ggtt = i915_vm_to_ggtt(vm);
-	unsigned first_entry = start >> PAGE_SHIFT;
-	gen6_pte_t __iomem *gtt_entries =
-		(gen6_pte_t __iomem *)ggtt->gsm + first_entry;
-	int i = 0;
-	struct sg_page_iter sg_iter;
-	dma_addr_t addr = 0;
+	struct sgt_iter sgt_iter;
+	gen6_pte_t __iomem *gtt_entries;
+	gen6_pte_t gtt_entry;
+	dma_addr_t addr;
 	int rpm_atomic_seq;
+	int i = 0;
 
 	rpm_atomic_seq = assert_rpm_atomic_begin(dev_priv);
 
-	for_each_sg_page(st->sgl, &sg_iter, st->nents, 0) {
-		addr = sg_page_iter_dma_address(&sg_iter);
-		iowrite32(vm->pte_encode(addr, level, true, flags), &gtt_entries[i]);
-		i++;
+	gtt_entries = (gen6_pte_t __iomem *)ggtt->gsm + (start >> PAGE_SHIFT);
+
+	for_each_sgt_dma(addr, sgt_iter, st) {
+		gtt_entry = vm->pte_encode(addr, level, true, flags);
+		iowrite32(gtt_entry, &gtt_entries[i++]);
 	}
 
 	/* XXX: This serves as a posting read to make sure that the PTE has
@@ -2462,10 +2459,8 @@  static void gen6_ggtt_insert_entries(struct i915_address_space *vm,
 	 * of NUMA access patterns. Therefore, even with the way we assume
 	 * hardware should work, we must keep this posting read for paranoia.
 	 */
-	if (i != 0) {
-		unsigned long gtt = readl(&gtt_entries[i-1]);
-		WARN_ON(gtt != vm->pte_encode(addr, level, true, flags));
-	}
+	if (i != 0)
+		WARN_ON(readl(&gtt_entries[i-1]) != gtt_entry);
 
 	/* This next bit makes the above posting read even more important. We
 	 * want to flush the TLBs only after we're certain all the PTE updates
@@ -3399,9 +3394,11 @@  struct i915_vma *
 intel_rotate_fb_obj_pages(struct intel_rotation_info *rot_info,
 			  struct drm_i915_gem_object *obj)
 {
+	const size_t n_pages = obj->base.size / PAGE_SIZE;
 	unsigned int size_pages = rot_info->plane[0].width * rot_info->plane[0].height;
 	unsigned int size_pages_uv;
-	struct sg_page_iter sg_iter;
+	struct sgt_iter sgt_iter;
+	dma_addr_t dma_addr;
 	unsigned long i;
 	dma_addr_t *page_addr_list;
 	struct sg_table *st;
@@ -3410,7 +3407,7 @@  struct i915_vma *
 	int ret = -ENOMEM;
 
 	/* Allocate a temporary list of source pages for random access. */
-	page_addr_list = drm_malloc_gfp(obj->base.size / PAGE_SIZE,
+	page_addr_list = drm_malloc_gfp(n_pages,
 					sizeof(dma_addr_t),
 					GFP_TEMPORARY);
 	if (!page_addr_list)
@@ -3433,11 +3430,10 @@  struct i915_vma *
 
 	/* Populate source page list from the object. */
 	i = 0;
-	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
-		page_addr_list[i] = sg_page_iter_dma_address(&sg_iter);
-		i++;
-	}
+	for_each_sgt_dma(dma_addr, sgt_iter, obj->pages)
+		page_addr_list[i++] = dma_addr;
 
+	GEM_BUG_ON(i != n_pages);
 	st->nents = 0;
 	sg = st->sgl;
 
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index a84625b..2314c88 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -706,7 +706,8 @@  struct get_pages_work {
 static void
 i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj)
 {
-	struct sg_page_iter sg_iter;
+	struct sgt_iter sgt_iter;
+	struct page *page;
 
 	BUG_ON(obj->userptr.work != NULL);
 	__i915_gem_userptr_set_active(obj, false);
@@ -716,9 +717,7 @@  struct get_pages_work {
 
 	i915_gem_gtt_finish_object(obj);
 
-	for_each_sg_page(obj->pages->sgl, &sg_iter, obj->pages->nents, 0) {
-		struct page *page = sg_page_iter_page(&sg_iter);
-
+	for_each_sgt_page(page, sgt_iter, obj->pages) {
 		if (obj->dirty)
 			set_page_dirty(page);